I don't know if I'd commit to anything more for GT2 after GT2+ is finished, I've spent more than four years on this one so far and there are plenty of other games out there[...]
Ah. Do you have any in mind? PS1 era, PS2, PS3?
Some that I thought would be cool with some light modding (though I guess not much bugfixing) would be adding some variations of cars to Need for Speed Hot Pursuit 2 (PS2 version), like the Diablo cop car that is only available on the other, inferior versions, or making all cars fully customizable on Midnight Club 3, like the Corvette, Elise and exotics. Maybe even a mod to port the PSP version of L.A. to PS2 using 3 as a base, for analog throttle/brakes, and better graphics, for a large-scale project.
Although I don't know if these games are easily moddable, and if it would be possible (probably not feasible) for the port to be made.
Do you prefer racing games, or do you have other genres in mind? Which specific games are easier to mod, and that are in need of bugfixing/beta content recovering?
EDIT: Oh! A smaller one I really wanted someone to do, is to port the hatchback spoilers from Need for Speed Underground 1 to Underground 2, maybe also Most Wanted and Carbon, if possible on those. Would that be complicated? I imagine the models would need tweaking for vehicles new to Underground 2.